1. Field of the Invention
The present invention relates to a magnetic disk memory device and, more specifically, to a housing having an improved structure for supporting a magnetic disk pack and a magnetic head positioner therein.
2. Description of the Related Art
A magnetic disk device has a magnetic disk pack which includes a plurality of magnetic disks coaxially stacked on a spindle with a predetermined spacing between each other, and a magnetic head positioner having a plurality of arms, each carrying a magnetic head. The arms and the disks are alternately arranged with each of the arms positioned in the spaces between the disks. One end of each of the arms is fixed on a second spindle. By rotating the second spindle back and forth by a specific angle around its axis, each of the magnetic heads is brought to a position over a desired magnetic track formed on the corresponding disk surface to read or write the information into the track.
Technical trends in recent development of the magnetic disk device are mainly oriented towards increasing the density of memories stored on the surface of the magnetic disk, and achieving a short access time to the stored memory. On the other hand, space allotted for the magnetic disk device in electronic devices is becoming small due to the trend of miniaturization of electronic devices. For example recent magnetic disk devices having an outer diameter of 21 cm and an inner diameter of 10 cm, the track density of the memory tracks on the disk surface has reached up to 1,000 tpi (tracks per inch), and the rotational speed of the disk has become as fast as 3,600 rpm.
The magnetic head should not make contact with the disk surface in order to avoid wearing and damaging both the disk and the magnetic head. However, it is desirable to keep the distance between the magnetic head and the disk surface as small as possible in order to increase the sensitivity of the magnetic head and to decrease the area of magnetic domain required for storing a bit, and hence to increase the bit density in the magnetic track. The gap between the magnetic head and the disk surface is known as the "flying height" in the art. In recent apparatus, the flying height has become as narrow as 0.2 .mu.m. Moreover the flying height must be kept constant, in order to maintain the constant sensitivity of the magnetic head, and to attain a stable operation of the device. It is, therefore, a very difficult bu important task to keep a constant flying height between the magnetic disk rotating with high speed, and to set the magnetic head precisely in a position over the desired magnetic track which has a narrow width, 25 .mu.m for example.
In order to keep precisely the relative position between the magnetic head and the magnetic track at a constant value, it is important to achieve a stable and smooth motion of both spindles of the magnetic disk pack and the magnetic head positioner. The supporting mechanism of both spindles and a housing for supporting them, is one of the crucial mechanisms for the magnetic disk devices. The housing for supporting the magnetic disk pack and these mechanisms has the additional function of a container to seal them from the ambient space and to protect them from dust and moisture. Accordingly, the design of the housing of the disk pack is important for improving the performance of the magnetic disk devices. The design also relates to the cost for assembling and adjusting the magnetic disk apparatus.
Generally, the housing of the magnetic disk pack is separated into two parts, a shell and cover, in order to install the disk pack inside. The shell supports mechanically the disk pack and the magnetic head positioner, while the cover seals the opening of the shell through which the magnetic disk and other mechanisms are installed.
FIG. 1 is a partial cutaway perspective view of an exemplary magnetic disk apparatus illustrating its general configuration. The housing 1 is divided into a shell 1A' and a cover 1B'. The shell and the cover are joined to each other at line 1a. It may be considered that the entire apparatus is composed of the part shown in FIG. 1 and another half part having almost symmetrical structure to that of FIG. 1.
In FIG. 1, 1A is a shell part of the housing for supporting the spindle 2 of a magnetic disk pack and a magnetic head positioner 3. Six magnetic disks 100 are assembled in a stack around the spindle 2. The number of the disks may be varied depending on the size of the memory to be stored in the apparatus. The spindle 2 is supported at both ends by ball bearings 7 and 8. These bearings contains a ferrofluidic seal which keeps airtight the space between the inside and outside separated by the bearing while assuring free rotation of the spindle 2. The magnetic disks 100 are spaced with a predetermined distance between each other and are rotated by the spindle 2, which is powered by a DC motor 4 attached to one end of the spindle 2. The magnetic head positioner 3 has a similar structure as that of the magnetic disk pack. The positioner 3 has arms (not completely shown) fixed to a spindle 5, which is supported by ball bearings 9 and 10. The spindle 5 is driven by a voice coil motor 6 to rotate about its axis to the left and right by a desired angle. So, the magnetic head (not shown) supported by arms is brought to a desired position over the magnetic disk.
Generally, the magnetic disk pack and the magnetic head positioner are supported at their opposite ends by bearings as shown in FIG. 1. Such double-ended support structure is superior than the single-ended support structure that supports the spindle by only one bearing attached to one end of the spindle, because the double-ended structure provides more stable operation of the device compared to the single-ended structure. Especially the former is better because it may be used regardless of the inclination of the axis of the spindle, vertical or horizontal for example, although in some cases, the spindle of the magnetic head positioner may be a single-ended structure. In the following disclosure, however, the explanation will be described with respect to a double-ended structure. It will be apparent that the disclosure may be easily applied to the single-ended structure as well.
As described before, the housing of the magnetic disk pack (simplified as "housing" hereinafter) is separated into two parts, the shell and cover, in order to install the disk pack therein. The housings of the prior art devices are summarized in several types depending on the cross-section of the housing, that is, the relationship between the housing and a cutting plane which intersects the housing to divide it into two parts. Typical cross-sectional types are schematically shown in FIGS. 2(a) through 2(d).
FIGS. 2(a)-(d) are schematic diagrams illustrating some of the typical ways the housing is separated into two parts by a cutting plane. FIG. 2(a) is a first type. The figure shows a cross section of a housing 1A, containing the disks 100, their spindle 2A and the spindle 5A of the magnetic head positioner (not shown completely). The housing 1A is mechanically separable into left and right parts at a border plane positioned vertically to the page at a line a--a. After the magnetic disks 100, their spindle 2A and the spindle 5A of the magnetic head positioner are installed into the housing 1A, the left and right parts of the housing are connected to each other. Details of such type of magnetic disk device are disclosed in, for example, U.S. Pat. No. 4,315,288, issued to Bernett et al. on Feb. 9, 1982.
In such configuration, both ends of the spindles of the magnetic disk pack and the magnetic head positioner (simplified respectively as "disk pack" and "head positioner" hereinafter) are supported by a pair of walls, each belonging to an opposite half of the housing respectively. Thus, the centers of the bearings which support the spindles at their opposite ends are apt to become eccentric from each other. The adjustment of there bearings is very critical, in order to keep tightly the magnetic head and the magnetic disk in respective desired position. Moreover, if both halves of the housing belong to different fabrication lots from each other, this sometimes raises a problem of thermal off-track caused by the difference in thermal expansion coefficient between the lots of the two halves of the housing.
Sometimes in order to avoid such difficulty, use of the single-ended type structure is adopted. However, as previously mentioned, the support stability of the spindles is insufficient. This problem increases when the number of spindles or the rotational speed of the disks is increased.
FIG. 2(b) is a schematic side view of a housing illustrating a second type of separation of the housing. As shown in the figure, the housing is separated into upper and lower parts between the spindle 2B of the disk pack and the spindle 5B of the head positioner. The words upper and "lower" or "left" and "right" with respect to the housing are relative, but such words will be used in the following description for the sake of identification. The cutting plane is positioned vertically to the page along a line b--b. The device shown in FIG. 1 belongs to this type. In the case of FIG. 2(b), slots 4B are provided on both opposite sides of the walls of the upper half of the housing 1B. The slot 4B is cut from the opening edge along the line b--b to the position of the spindle 2B in order to set the spindle at the position. In the figure, the spindle 5B is a single-ended type, so the slot is unnecessary for the spindle 5B. If the spindle 5B is to be supported at its opposite ends, however it would be necessary to provide another pair of slots in the lower half of the housing like slot 4B on the upper half of the housing.
in the type of FIG. 2(b), the spindles 2B and 5B of the disk pack and the head positioner are respectively installed in complementary halves of the housing, and are subsequently mechanically connected to each other. Thus, the adjustment for keeping the relative position between the magnetic head and the disk is very critical, although the problem of the thermal off-track described with respect to the type 1 is not overcome. Also, since the housing has slots cut in both side walls of the housing, the housing lacks rigidity. Finally, since the number of parts of the housing increases, the assembling cost also increases.
FIG. 2(c) shows schematically a side view of a third type of housing. The housing 1C is separated into left and right halves by a plane indicated by a line c--c, which passes through the centers of the spindles 2C and 5C of the disk pack and the head positioner. In the type of FIG. 2(c), the holes to support the spindles 2C and 5C are separated into two semicircles. This increases the difficulty of making the holes, and hence decreases the accuracy of roundness of the circle formed by combining these two semicircles. The rigidity of the housing to support the spindles 2C and 5C is decreased, and the disk pack sometimes may suffer from vibration. The thermal off-track problem is not overfed. Moreover, the engaging surfaces of the left and right halves of the housing are not a single plane because of the semicircles cut for the spindles. This increases the difficulty of inserting sealing means between the two halves of the housing which seal off the disk pack from the surrounding spaces. Thus, air tightness is often decreased.
FIG. 2(d) shows schematically a side view of a fourth type of the housing, in which the housing 1D is divided into a shell 1D' and a cover 1D" by a plane d--d which passes through a spindle 5D of the head positioner, and intersects the side of the housing diagonally. In this type, the side slots 4D for inserting the spindle 2D of the disk pack is necessary. In the type of FIG. 2(d), the spindle 5D is a single-ended type. More details of such a type as described in for example, U.S. Pat. No. 4,692,827 issued to Biermeier et al. which issued on Sep. 8, 1987. This type is intended to ease the difficulty in assembly of the device. However, the difficulties as described with respect to the types 2(b) still remain.
As has been described above, the structure of the prior art housing is directed to ease the assembly of the disk device. By doing so, they are intended to increase the accuracy of the assembled device. Accordingly, in many cases, the spindle, especially the spindle of the head positioner, is a single-ended type. The double-ended spindle is supported by a pair of holes which is divided into two parts by the intersection plane, or at least the hole is cut away at one side by the slot to insert the spindle. This causes a lack of rigidity of the housing and causes various problems described above.